Every station in the World Ocean Database that sampled to at least 100 m depth, flashing at its exact place and time. From HMS Challenger through isolated national expeditions, to the transoceanic collaboration of the postwar decades, to Argo's drifting floats.

It starts with HMS Challenger (1872-76), widely considered the voyage that founded oceanography as a scientific discipline. For decades after, exploration stayed fragmented: individual nations running their own campaigns, mapping the waters off their own coasts, largely working in isolation from one another.

Watch what happens from the 1940s onward. The pattern shifts from scattered dots to long, arrow-straight lines, the signature of transoceanic research cruises, genuine international collaboration replacing isolated national effort. It starts concentrated in the North Atlantic and North Pacific before gradually reaching the rest of the global ocean.

Data: World Ocean Database (NOAA NCEI)